Chemical Composition, Antioxidant, and Antibacterial Activities of <i>Mezilaurus duckei</i> (Lauraceae)

Mezilaurus duckei, a Brazilian endemic tree species found exclusively in the Amazon Rainforest, is primarily exploited for timber in construction. Due to its endangered status, this study aimed to investigate the chemical profile and biological properties of the ethanolic extract and its phases derived from M. duckei leaves. Chemical profiling using high-performance liquid chromatography-tandem mass spectrometry revealed flavonoids, including glycosylated kaempferol and its derivatives, as well as γ-butyrolactones, as the major constituents. Additional chromatographic separations led to the isolation of kaempferol, reported for the first time in the Mezilaurus genus, and rubrenolide, identified for the first time in M. duckei. Antioxidant activity, assessed using the 2,2-diphenyl-1-picrylhydrazyl method, demonstrated significant free radical scavenging properties of the ethanolic extract (half-maximal inhibitory concentration [IC₅₀] = 1.43 µg/mL) and the ethyl acetate phase (IC₅₀ = 1.28 µg/mL). Antimicrobial activity, evaluated via the microdilution method, revealed promising activity of the dichloromethane fraction against S. aureus and E. coli (minimum inhibitory concentration values of 185.5 and 375 µg/mL, respectively). Toxicity assessment using the Artemia salina lethality assay confirmed the non-toxic nature of the ethanolic extract (50% lethal dose > 1000 µg/mL). These results highlight the potential of M. duckei as a source of bioactive compounds, undescoring their relevance for further applications.